Perfusion index smoother

ABSTRACT

An embodiment of the present disclosure seeks to smooth a perfusion index measurement through use of a baseline perfusion index measurement and/or through the use of multiple PI calculations. The combination of the baseline perfusion index measurement reduces an error between a calculated measurement of PI and actual conditions.

PRIORITY CLAIM TO RELATED PROVISIONAL APPLICATIONS

The present application is a continuation of U.S. application Ser. No.13/627,855, filed Sep. 26, 2012, entitled “Perfusion Index Smoother,”which is a continuation of U.S. application Ser. No. 11/871,620, filedOct. 12, 2007, entitled “Perfusion Index Smoother,” now U.S. Pat. No.8,280,473, which claims priority benefit under 35 U.S.C. §119(e) of U.S.Provisional Application Ser. No. 60/851,346, filed Oct. 12, 2006,entitled “Perfusion Index Smoother,” which is incorporated herein byreference.

RELATED CASES

The present application is related to U.S. Pat. Nos. 6,334,065,6,606,511 and the continuation, continuation-in-part, and divisionalapplications thereof. The foregoing disclosure is incorporated herein byreference and included in the present filing.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates in general to patient monitoring and inparticular to oximeter patient monitors capable of determining perfusionindex measurements.

2. Description of the Related Art

Oximeter systems providing measurements of a monitored patient havebecome the standard of care in many patient care settings, includingsurgical, post surgical, neonatal, general ward, home care, physicaltraining, and the like. In general, oximeter systems accept one or morenoninvasive signals from an optical sensor or probe capable of emittingmultiple wavelengths of light into a tissue site and capable ofdetecting light after attenuated by the tissue site. The optical sensorgenerally outputs intensity signal data. FIG. 1 illustrates aphotoplethysmograph intensity signal 100 output by an oximeter sensor.An oximeter does not directly detect absorption, and hence does notdirectly measure a standard plethysmograph waveform. However, thestandard plethysmograph can be derived by observing that the detectedintensity signal 100 is merely an out of phase version of an absorptionprofile known to one of skill in the art. That is, the peak detectedintensity 102, generally corresponds to a minimum absorption, andminimum detected intensity 104, generally corresponds to a maximumabsorption. Further, a rapid rise in absorption during an inflow phaseof the plethysmograph is reflected in a rapid decline 106 in intensity.Likewise, a gradual decline in absorption during the outflow phase ofthe plethysmograph is reflected in a gradual increase 108 in detectedintensity.

FIG. 2 illustrates a flow calculator 200 which receives a processedsignal 202 responsive to at least one of the intensity signals outputfrom the sensor. In an embodiment, the flow calculator outputs anindication of blood flow, such as, for example, a perfusion index (PI)204. In an embodiment, the PI 204 comprises a relative indication ofpulse strength at a monitoring site. For example, the PI 204 may bedefined as the ratio of the wavelength's (A) AC signal to the DC signal,or the percentage of pulsatile signal to non-pulsatile signal, accordingto the following:

PI=(λ_(max)−λ_(min))/λ_(DC)

where λ_(max) is the maximum value, λ_(min) is the minimum value, andλ_(DC) is the average value of the signal 202.

Once calculated, the PI 204 may advantageously be displayed in a widenumber of ways, including rising LEDs or other display elements, text,graphics, or other visual elements including color, flashing, and thelike, trended data, trace data, or the like. FIG. 3A illustrates adisplay output for an oximeter patient monitor 302 including a textualPI display 304 (shown as “3.25 PI”) ranging from 1.0 to 20. FIG. 3Billustrates a display output for a handheld oximeter patient monitor 322including a PI bar 324 ranging from, for example, “<0.1%” to “>5%” withsteps of “<0.1%,” “0.25%,” “0.5%,” “1%,” “1.25%,” “1.5%,” “1.75%,” “2%,”“3%,” and “>5%.” An artisan will recognize from the disclosure hereinthat various steps and a wide variety of scalars or other mathematicalmapping can be used to make PI numbers more readily understandable to acaregiver. However, using the foregoing scale, the PI bar 324 can beused as a diagnostic tool during low perfusion for the accurateprediction of illness severity, especially in neonates. Moreover, therate of change in the PI bar 324 can be indicative of blood loss, sleeparousal, sever hypertension, pain management, the presence or absence ofdrugs, or the like. According to one embodiment, a measurement belowabout “1.25%” may indicate medical situations in need of caregiverattention, specifically in monitored neonates. Because of the relevanceof about “1.25%”, the PI bar 324 may advantageously include levelindicia that switch sides of the PI bar 324, thus highlighting anyreadings below about that threshold. Moreover, behavior of the PI bar324, as discussed below, may advantageously draw attention to monitoredvalues below such a threshold.

The PI bar 324 may advantageously activate LEDs from a bottom toward atop such that the bar “fills” to a level proportional to the measuredvalue. In one embodiment, the PI bar 324 shows a static value ofperfusion for a given time period, such as, for example, one or morepulses. In another embodiment, or functional setting, the PI bar 324 mayadvantageously pulse with a pulse rate, may hold the last reading andoptionally fade until the next reading, may indicate historical readingsthrough colors or fades, traces or the like. Additionally, the PI bar324 may advantageously change colors, flash, increasingly flash, or thelike to indicate worsening measured values of perfusion.

As discussed above, the monitors 302, 322 may include outputfunctionality that outputs, for example, trend perfusion data, such thata caregiver can monitor measured values of perfusion over time.Alternatively or additionally, the monitors 302, 322 may displayhistorical trace data on an appropriate display indicating the measuredvalues of perfusion over time. In an embodiment, the trend data isuploaded to an external computing device through, for example, amultipurpose sensor connector or other input output systems such as USB,serial or parallel ports, computing networks, or the like. Additionalinformation regarding the calculation and use of PI is disclosed in the'065 patent, assigned to Masimo Corporation (“Masimo”) of Irvine,Calif., and incorporated by reference herein.

SUMMARY OF THE DISCLOSURE

Aspects of the present disclosure include a system which provides a moreaccurate indication of PI. In one embodiment, the wavelength used todetermine PI is in the infrared (IR) spectrum. IR wavelengths are moreindependent of saturation than are wavelengths in the Red (R) spectrum.As a result, when the saturation changes, the PI calculated from a Rwavelength tends to vary greater than the PI calculated from a IRwavelength. Although the IR intensity signal data is less responsive tosaturation than various other intensity channels, the IR intensitysignal remains somewhat susceptible to motion-induced noise, distortionand the like. In general, PI measurements during lower signal quality ordistortion generally trends the PI too high. As understood by an artisanfrom the disclosure herein, higher PI measurements should correlate tobetter perfusion through the tissue site, and lower PI measurementsshould correlate to lower perfusion through the tissue site. Thus, noisemay cause a patient monitor to give a caregiver the indication that apatient has better perfusion through a measurement site than is actuallythe case.

Based at least thereon, embodiments of the present disclosure seek toreduce an error between a calculated measurement of PI and actualconditions. In an embodiment, a baseline perfusion index (“baseline PI”)is determined and used to improve measurements during motion conditions.For example, a smoother may advantageously determine a baseline PIduring strong signal quality, high signal confidence conditions, and usethat baseline PI or a statistical combination of baseline PIs instead ofor in addition to the current PI that is being influenced by noise. Inan embodiment, the smoother selects the lower PI value as the output PIvalue. This is because motion noise tends to increase PI, thus the lowerPI value tends to be the more accurate value.

In an embodiment, PI is calculated using at least two differentcalculation techniques. The two different calculations are analyzed anda PI indication is determined. In an embodiment, the lower of the two PIvalues is chosen. In an embodiment, the PI values are averaged orstatistically analyzed to determine a more accurate value for PI.

In an embodiment, a method of smoothing a perfusion index measurement inan oximeter system is disclosed. The method includes the steps ofestablishing a baseline perfusion index during quality signal conditionsof a signal responsive to intensity signals acquired from a detectorcapable of detecting light attenuated by body tissue and leveraging thebaseline perfusion index during poor signal conditions. In anembodiment, leveraging includes outputting the baseline perfusion indexwhen a current perfusion index measurement is higher than the baselineperfusion index. In an embodiment, leveraging includes outputting acurrent perfusion index measurement when the baseline perfusion index ishigher than the current perfusion index measurement. In an embodiment,the signal is responsive to an IR intensity signal.

In an embodiment, an oximeter is disclosed. The oximeter includes aninput capable of receiving intensity signal data responsive to intensitysignals acquired from a detector capable of detecting light attenuatedby body tissue, a memory storing a baseline Perfusion Index (PI) and aprocessor programmed to output the baseline PI when the signal dataincludes motion-induced noise and a current PI derived from the signaldata is not lower than the baseline PI. In an embodiment, an alarm isincluded which is configured to alert a caregiver when the output meetspredetermined criteria. In an embodiment, the processor is programmed tooutput the current PI when the signal data is relatively calm or whenthe current PI is lower than the baseline PI.

In an embodiment, a method of determining an indication of perfusionindex in a patient monitor is disclosed. The method includes the stepsof receiving plethysmographic data, calculating two or more indicationsof perfusion index using at least two different calculation techniques,and determining a final indication of perfusion index based on theindications of perfusion index. In an embodiment, the final indicationof perfusion index is determined by selecting the lowest indication ofperfusion index. In an embodiment, the final indication of perfusionindex is determined by statistical analysis. In an embodiment, the finalindication of perfusion index is determined by averaging the indicationsof perfusion index.

In an embodiment, a method of determining an indication of perfusionindex is disclosed. The method includes the steps of receivingplethysmographic data and determining an indication of perfusion indexby utilizing at least one calculation techniques to determine aresulting indication of perfusion index. In an embodiment, determiningthe indication of perfusion index includes utilizing the calculationtechnique that will result in the lowest perfusion index value.

In an embodiment, an oximeter is disclosed. The oximeter includes aninput capable of receiving intensity signal data responsive to intensitysignals acquired from a detector capable of detecting light attenuatedby body tissue, a first calculator configured to calculate a firstindication of perfusion index using a first calculation technique, asecond calculator configured to calculate a second indication ofperfusion index using a second calculation technique and a processorconfigured to utilize at least one of the first and second calculatorsto determine a resulting indication of perfusion index. In anembodiment, the processor is configured to select the calculator whichcalculates the lowest indication of perfusion index. In an embodiment,the processor utilizes both calculation techniques. In an embodiment,the processor is further configured to select the lowest indication ofperfusion index as the resulting indication of perfusion index.

In an embodiment, a method of determining an indication of aphysiological condition using data responsive to intensity signalsacquired from a detector capable of detecting light attenuated by bodytissue is disclosed. The method includes the steps of determining one ormore indications of pulse information from data responsive to intensitysignals acquired from a detector capable of detecting light attenuatedby body tissue, determining a first indication of amplitude data for asingle pulse based on the one or more indications of pulse information,determining a second indication of amplitude data for a plurality ofpulses based on the one or more indications of pulse information,determining a final indication of amplitude data based on the first andsecond indications and outputting the final indication. In anembodiment, the amplitude data is used to determine an indication ofperfusion. In an embodiment, determining a final indication includesselecting the lowest indication of amplitude from the first and secondindications of amplitude. In an embodiment, determining a finalindication includes averaging the first and second indications ofamplitude. In an embodiment, determining a final indication is based ona statistical analysis of the first and second indications of amplitude.In an embodiment, the combination includes an averaged combination ofpulses. In an embodiment, the combination includes a maximum and minimumamplitude of a plurality of pulses. In an embodiment, the combinationincludes a statistical combination of pulses.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the disclosure have been described herein. Ofcourse, it is to be understood that not necessarily all such aspects,advantages or features will be embodied in any particular embodiment ofthe disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A general architecture that implements the various features of thedisclosure will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the disclosure and not to limit its scope.

FIG. 1 illustrates a graph showing an intensity “plethysmograph”oximetry waveform.

FIG. 2 illustrates a flow calculator capable of determining measurementsfor a perfusion index.

FIGS. 3A-3B illustrate patient monitors capable of calculating anddisplaying the measurements of FIG. 2.

FIG. 4 illustrates a simplified block diagram of a smoothed perfusionindex generator, according to an embodiment of the disclosure.

FIG. 5 illustrates a flow chart of a smoothing process, according to anembodiment of the disclosure.

FIG. 6 illustrates another embodiment of a simplified block diagram of asmoothed perfusion index generator.

FIG. 7 illustrates a simplified block diagram of an embodiment of a PIdetermination system using multiple PI calculation techniques.

FIG. 8 illustrates a flow chart of a PI decision process, according toanother embodiment of the disclosure.

DETAILED DESCRIPTION

FIG. 4 illustrates a simplified block diagram of a smoothed perfusionindex generator 400, according to an embodiment of the disclosure. Asshown, the generator 400 includes a flow calculator 402, ad smoother 404and optional indications of noise, including a measure of distortion406, signal quality 408, and waveform quality 410. In an embodiment, adata signal 420 responsive to an intensity signal is input into the flowcalculator 402, and a current value 422 of PI is calculated. A skilledartisan will recognize a number of calculations that can determinevalues of perfusion, including, for example, the foregoing ratio of theAC signal to the DC signal. The current value 422 of PI, which in anembodiment is subject to noise and distortion in the data signal 420, isinput into the smoother 404, which reduces an error between the currentvalue 422 of PI and actual perfusion conditions. For example, thesmoother 404 may advantageously determine a baseline PI, and dependingupon an indication of some or all of an amount of distortion, noise,signal quality, and/or waveform quality in the data signal 422,substitute or combine the baseline PI for or with the current value 422to generate an output PI 430.

In an embodiment, the wavelength used to determine PI is in the infrared(IR) spectrum. IR wavelengths are more independent of saturation thanare wavelengths in, for example, the Red (R) spectrum. As a result, whenthe saturation changes, the PI calculated from a R wavelength tends tovary greater than the PI calculated from a IR wavelength.

In an embodiment, the distortion signal 406 may comprise a Boolean valueindicating whether the data signal 422 includes, for example,motion-induced noise. Although an artisan will recognize from thedisclosure herein a number of methodologies for deriving the distortionsignal 406, derivation of a Boolean distortion signal is disclosed inU.S. Pat. No. 6,606,511, incorporated herein by reference.Alternatively, or in addition to, the signal quality signal 408 maycomprise a Boolean value indicating whether the data signal 422 meetsvarious waveform criteria Although an artisan will recognize from thedisclosure herein a number of methodologies for deriving the signalquality signal 408, derivation of a Boolean distortion signal isdisclosed in the '511 patent. Alternatively, or in addition to, afeature extractor 440 may advantageously produce waveform qualityoutputs 410, indicative of waveform quality or waveform shape. Althoughan artisan will recognize from the disclosure herein a number ofmethodologies for deriving the waveform quality signal 410, derivationthereof is disclosed in the '065 patent.

Thus, the smoother 404 accepts one or more or different indicators ofthe quality of the data signal 420, and determines how to smooth the PIoutput to reduces errors between data trends and actual perfusionconditions. In an embodiment, the smoothing may advantageously comprisestatistical weighting, other statistical combinations, or simply passingthe PI 422 through to the output, depending upon one or more of thequality signals 406, 408, 410, or logical combinations thereof. In anembodiment, the smoother 404 selects the lowest PI value to pass to theoutput PI 422. This is because motion noise tends to increase PI, thusthe lower PI value tends to be the more accurate value.

Upon the output of a smoothed PI measurement, a monitor mayadvantageously audibly and/or visually presents the measurement to acaregiver, and when the measurement meets certain defined thresholds orbehaviors, the monitor may advantageously audibly and/or visually alertthe caregiver. In other embodiments, the monitor may communicate withother computing devices to alert the caregiver, may compare longer termtrend data before alarming, or the like.

FIG. 5 illustrates a flow chart of a smoothing process 500, according toan embodiment of the disclosure. In block 502, data is acquiredresponsive to one or more of multiple channel intensity signals. Inblock 504, a determination is made whether distortion is present,whether signal quality is good, whether there is motion-induced-noise orthe like. When acceptable noise levels exist, in block 506, the baselinePI becomes the current PI and in block 508, the baseline PI is output.However, when unacceptable signal quality or the like is detected, thecurrent PI is compared to the baseline PI. When the current PI issmaller than the baseline PI, in block 506, the baseline PI becomes thecurrent PI. However, when the current PI is greater than or equal to thebaseline PI, the baseline PI is output in block 510. Thus, the smoothingprocess 500 determines when a baseline PI can be acquired in qualitymonitoring conditions, and then uses that baseline PI to avoid drift orother errors that may deteriorate the accuracy of the PI output. Anartisan will recognize from the disclosure herein that the baseline PIcould be reset periodically, some or all iterations, when otheroccurrences or measurements suggest a reinitialization, when varioustrends occur, or the like.

FIG. 6 illustrates another embodiment of a simplified block diagram of asmoothed perfusion index generator 600. As shown, the generator 600includes a smoother 604 and optional indications of noise, including ameasure of distortion 606, signal quality 608, waveform quality 610, andPleth Feature Extractor similar to those described with respect to FIG.4. In an embodiment, a data signal 620 responsive to an intensity signalis input into the PI Analyzer 602, and a PI value 422 is outputted foruse by the smoother 604. In an embodiment, the PI Analyzer employsmultiple different calculation techniques to determine a more accurateindication of PI. In an embodiment, based on the indications ofdistortion signal quality, waveform quality and/or other indications ofsignal quality, a specific calculation technique is used to determine aPI output value 622.

FIG. 7 illustrates a simplified block diagram of an embodiment of a PIdetermination system 700 using multiple PI calculation techniques. Asshown, pleth data 720 is input into the system. The pleth data 720 isthen routed to at least two different PI calculators 702, 704. In anembodiment, more than two different types of calculation techniques canbe used. The at least two PI calculators 702, 704 output PI indicationsfor input into the PI selector 706. The PI selector 706 determines a PIvalue to output. In an embodiment, the PI selector chooses the lowest PIvalue. In general, the lower PI value should be the more accurate value,particularly in the presence of motion induced noise. This is becausemotion induced noise tends to raise PI values. In an embodiment, the PIselector 706 averages or otherwise analyzes the PI values usingstatistical modeling in order to determine a more accurate value of PI.

In an embodiment, one of the PI calculators 702, 704 determines a PIvalue based on pulse by pulse determination of PI, such as, for example,using the following PI formula as described above:

PI=(λ_(max)−λ_(min))/λ_(DC)

In an embodiment, one of the PI calculators 702, 704 determines a PIvalue based on a fixed or variable interval of pleth data including morethan one pulse, in effect calculating a bulk PI.

FIG. 8 illustrates a flow chart of a PI decision process 800, accordingto another embodiment of the disclosure. At block 802, the process 800receives pleth data 802. The process then moves to block 804 where theprocess 800 calculates at least two different PI indications, such as,for example, as described with respect to FIG. 7. The process 800 thenmoves to block 806 where an indication of PI is determined based on thedifferent calculations, again, such as, for example, as described withrespect to FIG. 7. The process 800 then repeats itself for each PI valuedetermination.

While the above perfusion index determination system has been describedin certain embodiments herein, other embodiments of the presentdisclosure will be known to those of skill in the art from thedescriptions herein. Moreover, the described embodiments have beenpresented by way of example only, and are not intended to limit thescope of the disclosure. Moreover, those of skill in the art understandthat information and signals can be represented using a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that can bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

Those of skill in the art further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein can beimplemented as electronic hardware, computer software, or combinationsof both. To illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans can implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein can be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor can be a microprocessor, but in thealternative, the processor can be any conventional processor,controller, microcontroller, or state machine. A processor can also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein can be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module can reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or other form of storage medium known in the art. A storagemedium is coupled to the processor, such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium can be integral to the processor. Theprocessor and the storage medium can reside in an ASIC. The ASIC canreside in a user terminal, physiological monitor and/or sensor. Theprocessor and the storage medium can reside as discrete components in auser terminal, physiological monitor and/or sensor.

Although the foregoing disclosure has been described in terms of certainpreferred embodiments, other embodiments will be apparent to those ofordinary skill in the art from the disclosure herein. Additionally,other combinations, omissions, substitutions and modifications will beapparent to the skilled artisan in view of the disclosure herein.Moreover, it is contemplated that various aspects and features of thedisclosure described can be practiced separately, combined together, orsubstituted for one another, and that a variety of combination andsubcombinations of the features and aspects can be made and still fallwithin the scope of the disclosure. Furthermore, the systems describedabove need not include all of the modules and functions described in thepreferred embodiments. Accordingly, the present disclosure is notintended to be limited by the recitation of the preferred embodiments,but is to be defined by reference to the appended claims.

Additionally, all publications, patents, and patent applicationsmentioned in this specification are herein incorporated by reference tothe same extent as if each individual publication, patent, or patentapplication was specifically and individually indicated to beincorporated by reference.

What is claimed is:
 1. A method of determining an indication ofperfusion index in a patient monitor, the method comprising: receivingpleth data; calculating at least two indications of perfusion indexusing at least two different calculation techniques; and determining afinal indication of perfusion index based on the at least twoindications of perfusion index.
 2. The method of claim 1, wherein thefinal indication of perfusion index is determined by selecting thelowest indication of perfusion index.
 3. The method of claim 1, whereinthe final indication of perfusion index is determined by statisticalanalysis.
 4. The method of claim 1, wherein the final indication ofperfusion index is determined by averaging the at least two indicationsof perfusion index.
 5. A method of determining an indication ofperfusion index, the method comprising: receiving pleth data; anddetermining an indication of perfusion index by utilizing at least oneof a first calculation technique and a second calculation technique todetermine a resulting indication of perfusion index.
 6. The method ofclaim 5, wherein determining the indication of perfusion index comprisesutilizing the calculation technique that will result in the lowestperfusion index value.
 7. An oximeter comprising: an input capable ofreceiving intensity signal data responsive to intensity signals acquiredfrom a detector capable of detecting light attenuated by body tissue, afirst calculation calculator configured to calculate a first indicationof perfusion index using a first calculation technique; a secondcalculator configured to calculate a second indication of perfusionindex using a second calculation technique; and a processor configuredto utilize at least one of the first and second calculators to determinea resulting indication of perfusion index.
 8. The method of claim 7,wherein the processor is configured to select the calculator whichcalculates the lowest indication of perfusion index.
 9. The method ofclaim 7, wherein the processor utilizes both calculation techniques. 10.The method of claim 9, wherein the processor is further configured toselect the lowest indication of perfusion index as the resultingindication of perfusion index.
 11. A method of determining an indicationof a physiological condition using data responsive to intensity signalsacquired from a detector capable of detecting light attenuated by bodytissue, the method comprising: determining one or more indications ofpulse information from data responsive to intensity signals acquiredfrom a detector capable of detecting light attenuated by body tissue;determining a first indication of amplitude data for a pulse based onthe one or more indications of pulse information; determining a secondindication of amplitude data for a combination of pulses based on theone or more indications of pulse information; determining a finalindication of amplitude data based on the first and second indications;and outputting the final indication as an indication of perfusion index.12. The method of claim 11, wherein the amplitude data is used todetermine an indication of perfusion.
 13. The method of claim 11,wherein determining a final indication further comprises selecting thelowest indication of amplitude from the first and second indications ofamplitude.
 14. The method of claim 11, wherein determining a finalindication further comprises averaging the first and second indicationsof amplitude.
 15. The method of claim 11, wherein determining a finalindication is based on a statistical analysis of the first and secondindications of amplitude.
 16. The method of claim 11, wherein thecombination comprises an averaged combination of pulses.
 17. The methodof claim 11, wherein the combination comprises a maximum and minimumamplitude of a plurality of pulses.
 18. The method of claim 11, whereinthe combination comprises a statistical combination of pulses.